The present invention is directed to a syringe that includes a gas driven piston to force liquid medication from a syringe cartridge through a variety of injection nozzles. The nozzles include a traveling hidden needle which is retracted until the syringe is activated and then is extended to puncture the skin of the person injected. The invention also contemplates a needleless injection nozzle which will permit injection without a needle. Further, in accordance with the invention, a very short needle which only barely penetrates the skin to assist injection is provided. The syringe may be mechanically operated for loading or aspirating the syringe.
The use of needleless injection has two major advantages. First, there is a needle phobia that is astonishingly widespread. Therefore,an injector that doesn't use or present a needle can do a lot to dispel that stigma from a lot of people. Secondly, the use of needleless injection decreases the frequency of accidental needle sticking and thus reduce the risk of the spread of possibly disease among the people who would otherwise handle the used needle. Use of needleless injection reduces tissue trauma and the development of scar tissue.
Needleless injection is well known in the art. In World War II for example, there are stories about lines of soldiers who were given pneumatically aspirated needleless injections. This was done for mass production reasons of getting the most injections in the most people in the least amount of time. The injectors used were massive guns. These guns utilized compressed air of maybe 500 psi and therefore needed substantial pressure chamber or accumulation chambers in order to provide sufficient energy to drive the liquid medication or vaccine through the skin.
The art has recognized the advantages of needleless injection. For example, the Russian literature recognized that Soviet needleless injectors were used in anesthetic practice with 271 patients (1670 injections) for premedication, local anesthesia in all sorts of surgical procedures, in primary surgical treatment of wounds, in bone fractures and for administration of analgesics during the postoperative period. Effects supervened 2-3 times more rapidly and the doses were 2-5 times smaller than when an ordinary syringe with a needle was used. Needleless injectors have definite advantages over syringes.
Further, the German literature has noted that when looking for new techniques of insulin applications which could replace the insulin syringe, we examined the possibility of using a dosable jet injector (Med. E Jet Injector) for dosing precision and handling as well as for bioavailability of insulin by measuring plasma insulin and blood glucose effects whereby syringe injection and jet injection were compared. In the following, we tested the compatibility of this latter type of application. Jet injection of insulin turned out to be more precise and compatibility at the site of a single test was good. The insulin appeared faster in the blood and accordingly disappeared faster after application of regular insulin (Alt-Insulin CS, Hoechst) and of crystalline intermediate acting insulin (Monotard MC, Novo) or of acid intermediate acting insulin (Depotinsulin CS, Hoechst). Blood glucose and C-peptide as a measure of B-cell function inhibition decreased more rapidly. This fact points to a faster kinetic after insulin jet injection. Hence, the jet injection technique is basically suited for insulin application. When changing over from syringe to jet injection differences in kinetics have to be considered.
Thus, the art has recognized both the advantages and the benefits that are gained through the use of needleless injection. There are known needleless injectors with many different mechanical methods of operation. For example, there are commercially available needleless insulin injectors that use spring power to provide the injection force. These devices generally require complicated manipulation before they are ready to use. There is still a need for a self-contained compact versatile injection syringe that can be used to give an individual injection utilizing a needleless injection nozzle and be used to give injections with minimum needle exposure and use.